An example of a conventional inertial sensor is shown in FIG. 13. In this inertial sensor, a mass member 500 is fixed to a basement layer by a support 502 via a beam 501. The mass members 500 on the left and right vibrate in opposite phases in an X-axis direction, and move in a Z-axis direction when an angular rate about a Y axis or an acceleration in a Z direction (detecting direction) is applied. An amount of the movement in the Z-axis direction is detected by a detecting member 504 as an angular rate or an acceleration.
A driving member 503 of this kind of inertial sensor is formed by a capacitive element in which a fixed electrode part and a movable electrode part are arranged so as to have their comb teeth engaged with each other, and a electrostatic attractive force is alternately generated between the fixed electrode part and the movable electrode part by applying a driving signal of alternative current having a proper phase difference with a bias voltage of direct current across the fixed electrode part and the movable electrode part, so that the mass members 500 on the left and right are vibrated in opposite phases to each other.
Further, the detecting member 504 has the mass member 500 as a movable electrode, and a fixed electrode is arranged on the basement layer side so as to face to the movable electrode part so that a detected signal in accordance with the angular rate and the acceleration is outputted by detecting the amount of movement in the Z direction of the mass member 500 as a capacitance change.
Here, the mass members 500 on the left and right are vibrated in opposite phases to each other, and thus the amount of movement in the Z direction by Coriolis force also has opposite phases when an angular rate about the Y axis is applied. However, in the case where an acceleration in the Z-axis direction is applied, the mass members 500 are moved in the Z-axis direction in the same phase regardless of the vibration in the X-axis direction. Therefore, the applied acceleration can be measured by adding the capacitance change signals detected from the two mass members to one another. Moreover, an acceleration component can be eliminated by subtracting the capacitance change signal from another, thereby measuring the applied angular rate.
For example, an angular rate sensor known from Japanese Patent Application Laid-Open Publication No. 2004-004119 (Patent Document 1) has a configuration where a pair of mass members arranged on a basement layer are vibrated in opposite directions to each other, so that an acceleration component is eliminated with accuracy when detecting a differential of yaw rates detected from the respective two mass members.
Further, a mechanical quantity detecting device known from Japanese Patent Application Laid-Open Publication No. 2002-188923 (Patent Document 2) has a configuration where a pair of mass members arranged on a basement layer are vibrated (tuning-fork vibration) in opposite phases to each other, so that an applied angular rate and an acceleration works in a detecting direction are separated by comparing a difference in phases of signals respectively detected from the two mass members.
Moreover, an angular rate sensor described in WO02/066927 (Patent Document 3) is formed by a drive frame, a Coriolis frame, and a detection frame, where the drive frame is supported by a beam that is flexible in a driving direction and rigid in a detecting direction, thereby easily moving in the driving direction and hardly moving in the detecting direction.